OS 10.5 - Application Freezing, No Screensaver & Other issues.

Ok, so now I've been using Leopard for a bit of time, some issues have made themselves known.

The most annoying is that if I leave the computer untouched for more than about 10 minutes (like watching a video), the active application will "freeze". The curser won't change, and will move normally, and the rollover effects (like Dock magnification and the "x, -, +" buttons) still work; but trying to interact with it in any way doesn't do anything. This usually lasts about 10 seconds and then it's good-2-go again.

A day or too ago, my screensaver stopped activating. I have it set up with a hot-corner, and to come on after 30 minutes of inactivity... neither will activate the screensaver. I've tried changing the screensaver, but it's same no-matter which one I want. It's not that big of a deal; I've just set the display to sleep instead, but I miss my pretty screensaver.

Also, a few days ago Front Row stopped working. It will activate normally, but within seconds the computer tries to go to sleep.

I had hoped 10.5.1 would fix some things, but it brought with it a new issue... it won't install! The computer goes to the blue screen, and a progress bar comes up with "configuring installation", and that's it. I even left it while I went for lunch, but it still hadn't progressed by the time I got back. I tried again later and the same thing.

When I first installed Leopard it went without a hitch, and the first problem (failing to wake from sleep) went away within a day, and it wasn't for a few days after that until the application freezing started.

Other than 10.5.1, all software is up-to-date.

Are these known issues with standard fixes? I really don't want to have to do a clean install...